Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. In hybrid vehicles, shorter engine operation times can lead to insufficient purging of fuel vapors from the vehicle's emission control system. To address this issue, hybrid vehicles may include a fuel tank isolation valve (FTIV) between a fuel tank and a hydrocarbon canister of the emission system to limit the amount of fuel vapors absorbed in the canister. In some examples, the FTIV may be a bi-stable valve adjustable between open and closed positions via a short electrical pulse. However, a position of the FTIV during use may not be known without an additional sensor. As a result, the FTIV may be adjusted into a different position than desired during operation.
One example approach of a bi-stable isolation valve is shown by Takagi et al. in U.S. Pat. No. 6,761,154. Therein, an electromagnetically actuated open/close valve is shown in a vapor passage between a fuel tank and a fuel canister. The valve is opened and closed under different engine operating conditions; however, there may not be a way of diagnosing a position of the valve.
As one example, the issues described above may be addressed by a method for adjusting a fuel tank isolation valve (FTIV) of a fuel system by sending an electrical pulse to the FTIV, and comparing a current draw of the FTIV to a known current draw profile to verify the position of the FTIV. In this way, the position of the FTIV may be diagnosed, thereby resulting in increased accuracy of subsequent valve control. Furthermore, the position of the FTIV may be verified during operation of the FTIV without depending on other sensors or components.
As another example, a method comprises adjusting a FTIV of a fuel system by sending electrical pulses to the FTIV, counting each of the electrical pulses to track a position of the FTIV, and using a canister temperature to verify the position of the FTIV when the position of the FTIV is unknown or invalid. In this way, the position of the FTIV may be verified using canister temperature, thereby resulting in increased accuracy of subsequent valve control and decreased emissions.
As yet another example, a fuel system comprises: an engine; a fuel tank; a canister for storing fuel vapors; a fuel tank isolation valve (FTIV) coupled in a vapor line between the fuel tank and the canister, the FTIV held in both opened and closed positions without any applied current; and a controller with computer readable instructions for diagnosing a position of the FTIV and subsequently adjusting the FTIV based on the diagnosed position and engine operating conditions. In this way, the position of the FTIV may be diagnosed regardless of engine operating conditions, thereby resulting in decreased emissions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.